1. Field of the Invention
The present invention relates to a process for the preparation of a thermoplastically processable aromatic polyamide.
2. Description of the Background
In principle, the preparation of thermoplastically processable aromatic polyamides are known (see, for example, DE-A-3,609, 011; Brode et al., Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 15, 761 (1974); Adv. Chem. Ser. (1975), 142; CA 84, 5530 sf). However, these aromatic polyamides have a high melt viscosity. Consequently, very high temperatures are necessary during their preparation and processing, usually at least 350.degree. C. At these temperatures, damage to the product is often observed, recognizable from discolorations or an impairment of the mechanical properties.
Aromatic polyamides are used as high temperature resistant materials in the aerospace, automobile, electrical and electronics industry, where they are exposed to temperatures in the region of 200.degree. C. and above in the presence of atmospheric oxygen. Under these conditions, discoloration of the product readily occurs with simultaneous diminution of the mechanical properties.
There have already been many attempts to redress these deficiencies. In particular, it has been proposed to carry out the polycondensation of the aromatic dicarboxylic acids and aromatic diamines in the presence of triphenyl phosphite or of an acid which has been derived from phosphorus having the formula:H.sub.3 PO.sub.m, where m is 2, 3 or 4 as catalyst and of a dialkylaminopyridine as cocatalyst (DE-A-3,539,846, 3,601,011, 3,609,011, 3,731,185, and German Patent Application number P 39 35 466.0). However, the resulting polyamides cannot always completely satisfy the prescribed requirements. A need therefore continues to exist for aromatic polyamides of improved properties.